1. Field of the Invention
The present invention concerns a wire wound electronic part used, for example, in mobile electronic equipments or thin electronic equipments.
2. Description of the Related Technology
Wire wound type electronic parts are used as step up circuit coils for DC/DC power sources in cellular phones or mobile electronic equipments such as digital still cameras and choke coils in peripheral circuits of various kinds of flat panel displays. For the application uses described above, it is particularly demanded for those having a small and low-profile dimension capable of high density mounting or low-profile mounting while ensuring desired inductor characteristics.
A wire wound electronic part has, for example, a core, terminal electrodes disposed to the core and a coil conductor wound around the core and connected at the ends thereof to the terminal electrodes. The core includes a wire wound core, an upper flange disposed to the upper end of the wire wound core and a lower flange disposed to the lower end of the wire wound core. A pair of the terminal electrodes are formed on the bottom of the lower flange of the core. Further, the coil conductor comprises a metal wire having an insulation coating formed at the outer circumference thereof and is wound around the periphery of the wire wound core of the core. Then, one and the other ends of the coil conductor are removed with the insulation coating and connected to the terminal electrodes respectively by soldering.
Japanese Unexamined Patent Publication No. 2002-334807 discloses a wire wound electronic part 110 as an example of the existent art. FIG. 5 is a vertical cross sectional view taken along a central axis of a wire wound core 111a showing the inner structure of the wire wound electronic part 110. FIG. 6 is an enlarged perspective view for a main portion showing a lower flange 111c of a core 111 used for the wire wound electronic part 110 as viewed on the side of the bottom 111B. Further, FIG. 7 is a vertical cross sectional view for a main portion showing the state of mounting the wire wound electronic part 110 on a circuit substrate 120.
As shown in FIG. 5 and FIG. 6, it specifically discloses a wire wound electronic part 110 including the core 111 having a columnar wire wound core 111a and flanges 111b, 111c formed at upper and lower ends thereof, a coil conductor 112 wound around the wire wound core 111a of the core 111, and terminal electrodes 116A, 116B disposed at a bottom 111B crossing the winding core part 111a of the flange 111c, in which both ends 113A, 1113B of the coil conductor 112 wound around the wire wound core 111a are conductively connected to the terminal electrodes 116A, 116B by using solders 117, 117. Then, a pair of grooves 115 are formed to the bottom 111B of the flange 111c, and the groove 115 has a bottom 115a, and moderate slopes 115b, 115b disposed on both lateral sides of the bottom 115a being slanted to the bottom 115a. Assuming a moderate slope 115b as a hypotenuse of a right triangle and defining the same with a length w2 for the bottom and a height in the vertical direction (hereinafter referred to as a vertical height) h2 of the right triangle, the length w2 for the bottom of the moderate slope 115b is formed larger than the vertical height h2 for the moderate slope 115b. Then, as shown in FIG. 6, the terminal electrode 116 has edge portions 116E1 to 116E3 on one of the moderate slopes 115b in the lateral direction of the groove 115 and is formed so as to extend by way of the flat surface 111C of the bottom 111B of the flange 111c to the outer lateral surface 111D of the flange 111c. 
In the existent wire wound electronic part 110, as shown in FIG. 5 and FIG. 6, the terminal electrode 116 decreases the thickness 116t as it approaches the edge portions 116E1 to 116E3 of the terminal electrode 116 in the lateral direction of the groove 115, and the position for the edge portions 116E1 to 116E3 of the terminal electrode 116 fluctuates in the lateral direction of the groove 115 on the moderate slope 115b. Therefore, the lateral size 116W for the terminal electrode 116 fluctuates depending on the position and is not stable.
Further, as shown in FIG. 7, upon mounting the wire wound electronic part 110 above a circuit substrate 120 in which a mounting land 122 is formed on a substrate 121, when solder 117 put between the flat surface 111C of the bottom 111B and the moderate slope 115b of the groove 115 of the flange 111c, and the mounting land 122 on the circuit substrate 120 on which the part is mounted is melted, the solder 117 moves in the lateral direction of the groove 115 along the moderate slope 115b of the groove 115 and the outer lateral surface 111D of the flange 111c. 
As described above, the distance between the flat surface 111C of the bottom 111B of the flange 111c and the mounting land 122 fluctuates as shown in FIG. 7 by the fluctuation of the lateral size 116W for the terminal electrode 116 and the movement of the molten solder 117 in the lateral direction of the groove 115.
Therefore, this results in a problem that the height and the attitude of the wire wound electronic part 10 becomes instable after mounting to the circuit substrate 120.